An end mill has been used for slot milling, shoulder milling or the like of a workpiece. In such milling, it is necessary to smoothly discharge chips generated by cutting. To this end, a plurality of chip discharging flutes is formed such that each chip discharge flute is formed between two peripheral cutting edges, thus enhancing chip discharging property. However, with a larger chip discharging flute, a minimum thickness (core thickness) of an end mill body becomes smaller so that rigidity of the end mill body is lowered. Accordingly, there has been a case where the end mill is broken at a proximal end portion of the end mill which is near rear ends of the chip discharging flutes of the end mill.
On the other hand, Patent Document 1 discloses an end mill where chip discharging flutes are made small on a rear portion of an end mill body so as to increase a cross-sectional area of the end mill body. With such a configuration, rigidity of the end mill can be enhanced so that the end mill can suppress deflection thereof whereby the end mill can perform cutting with high accuracy.
Such an end mill has been requested to possess higher breaking resistance and more improved chip discharging property.